Various forms of acne exist. These include: juvenile, which may emerge as of age 9 years, with no premonitory sign of puberty, and which affects approximately 70% of adolescents of both genders; adult, which, outside of the consequences of hormonal contraceptive treatment, corresponds, in fact, in most cases, to juvenile acne persisting in the absence of treatment of after inappropriate treatment; drug-related, the main causes of which are vitamin B12, systemic or local corticosteroids, iodine- or bromine-based preparations, androgens and androgenic progestogen contraceptive pills; neonatal, due to maternal androgens, and for which recovery is spontaneous; excoriated, of young girls, which is an exacerbation of normal and classic juvenile acne due to almost obsessive touching of acne spots.
Thus, most forms of acne derive more or less directly from juvenile acne. Acne is, in all likelihood, a multifactorial disease which can be summarized by the following triad: hyperseborrhea+disorder of keratinization of the pilosebaceous canal+a microbial factor.
Hyperseborrhea
There is no acne without hyperseborrhea and, broadly speaking, acne is proportional to the degree of seborrhea. Sebum secretion is under hormonal control and constitutes one of the best indicators of androgen levels explaining the emergence of acne at the time of puberty, during which a physiological hormonal explosion occurs.
The androgen hormone most involved in acne is testosterone. Gonadal testosterone circulates in the body in a protein-bound form and only free testosterone enters the target cell: the sebaceous gland. There, an enzyme, 5α-reductase, converts testosterone to its metabolite, dihydrotestosterone (DHT), which stimulates the synthesis of nuclear proteins. The more DHT which reaches the nucleus, the greater the increase in sebaceous gland size and proliferation. The glands fill with lipids and, since the sebaceous gland is a holocrine secretory gland, the greater the quantity of excreted sebum.
Keratinization Disorder of the Pilosebaceous Canal
This point constitutes a sine qua non condition for the occurrence of acne. The epithelium bordering the pilosebaceous canal at infra-infundibulum level then forms a large quantity of abnormally keratinized cells, a large quantity of keratin and a particularly sparingly soluble intercellular ground substance. At infra-infundibulum level, this creates a compact plug which prevents expulsion of the sebum: this is the microcyst or closed comedo stage, the true elementary lesion of acne. The microcyst can then evolve in 2 ways: either the keratin and sebum continue to provoke swelling of the microcyst forcing dilation of the acro-infundibulum, thus forming an open comedo or common blackhead, with no real seriousness; or the wall of the microcyst ruptures with irruption into the dermis of sebum, keratin and free fatty acids. An inflammatory reaction occurs, which is exacerbated by the last component in the etiology of acne.
Microbial Factor
Normally, in the pilosebaceous follicle, 3 types of microorganism exist: a yeast: Pityrosporum ovale, whose pathogenic role in acne appears nil, a non-pathogenic white Staphylococcus, an anaerobic bacteria, diphtheroid and Gram-positive: Corynebacterium acnes (formerly called Propionibacterium acnes), which synthesizes a lipase able to hydrolyze the triglycerides of sebum into free fatty acids that are irritants for the dermis. This microorganism is also involved in the local production of protease, hyaluronidase and neuraminidase, which exacerbate the inflammatory process cited above.
The data presented above are derived from a review of the following documents: F. Poli (1996): Acné prépubertaire, Le Concours Médical, 118:905–908; P. Morel (1981), polycopié de dermato et vénéro, Le Kremlin Bicêtre: 161–179; Francois Daniel (1977): Dermatologie pratique, Edition Dupuy-Compton Medical, Neuilly. Both during adolescence and adulthood, acne induces a negative self-image in people who have acne-prone skin. The cosmetic industry is thus within its scope when it proposes a new approach to resolving the problems of acne-prone skins.